1. Field of the Invention
The present invention relates to an image display apparatus of a dot matrix type, such as a liquid crystal display, which is capable of suitably displaying any format of Image signal which is input.
2. Description of the Related Art
Conventionally, raster scan type CRTs have been widely used for image displays for computers. This CRT display receives from a computer a video signal including an analog video signal containing a vertical synchronization signal and horizontal synchronization signal mixed together to display a desired image.
Also, recently, displays using liquid crystal panels (LCD) have come under attention from the viewpoints of space-saving, energy-saving, lower costs, etc. A liquid crystal panel is a display of a dot matrix type wherein pixels are of a fixed size and each pixel is supplied with voltage separately to separately control them for the display.
There are many types of video signals depending on the resolution, input frequency, etc. For example, as the resolution, there are 640xc3x97480 (horizontal pixelsxc3x97vertical pixels (same below)), 720xc3x97400, 800xc3x97600, 1024xc3x97768, 1152xc3x97864, 1280xc3x971024, etc. Furthermore, even among signals of the same resolution of 1280xc3x971024, there are a large number of frequencies of signals, such as 64 kHz/60 Hz (horizontal frequency/vertical frequency (same below)), 80 kHz/75 Hz, 91 kHz/85 Hz, 81 kHz/77 Hz, etc.
For the specifications of these video signals, those established by the Video Electronics Standard Association (VESA) are widely known.
Although there are many types of video signals as explained above, many computer displays recently used are so-called xe2x80x9cmulti-syncxe2x80x9d types, that is, are not limited to the type of video signal and are capable of automatically handling a plurality of types of video signals and suitably displaying the image.
A multi-sync type display is ordinarily designed to detect characteristics relating to specifications of a video signal, such as the state of a synchronization signal, from an input video signal, compare the characteristics with the specifications of video signals registered in advance to identify the type of the video signal, adjust a drive cycle and amplitude of scanning lines of the display so as to match with a synchronization signal of the video signal based on the identified results, and display an image in accordance with the video signal.
However, an unregistered type of video signal is sometimes input to a multi-sync display handling a plurality of types of video signals by this method.
In such a case, up until now, the method has been taken of selecting the video signal of the closest specifications among the registered video signals and controlling the display circuit based on the specifications of that video signal or of preparing default data and controlling the display circuit by using the default data when there is no matching video signal.
Also, the VESA has established a method of determining a signal timing of a not registered signal as the GTF (generalized timing formula). The method of controlling the display circuit based on this method is also being taken.
To display an analog image signal on a display of a dot matrix type, the input image signal has to be sampled at predetermined sampling intervals to convert it from an analog to digital format and made to match with the number of horizontal and vertical pixels of the display. If the number of pixels matches and the pixels are properly controlled, basically there will be almost no effect due to the differences of displays and a stable output can be expected. If the number of horizontal and vertical pixels do not match between the signal and the display, however, proper display is no longer possible.
Note that the information on the dot intervals in the horizontal direction of image signals for such a signal conversion is called a xe2x80x9cdot clockxe2x80x9d. This information is also included in the VESA standard. In a CRT or raster scan type display, however, display is possible even without knowing the precise number of dots in the horizontal direction. Therefore, this is a parameter which is not ordinarily used for display.
In a dot matrix type multi-sync display, an image sometimes cannot be properly displayed by the conventional method of processing explained above when a non-registered video signal is input.
In the method of using the specifications of the video signal having the closest specifications to the characteristics of the detected input signal, the disadvantages sometimes arise that a signal is processed as a signal having a different resolution (number of valid pixels) just because the horizontal and vertical frequencies happen to be close, that there is no registered signal of a close frequency, the signal is processed as a signal having a little distant frequency, and the position of the image shifts, or that the scaling rate is not suitable and therefore the image overflows from the screen or conversely becomes remarkably smaller than the screen.
Further, in the method of using default data, the method works well when the signal is close to the default data, but when this is not so, the signal sometimes will not match it at all and proper display will not be possible.
Also, the GTF only establishes the time and does not include information of the dot clock frequency, so while it is useful in determining operations of a deflection circuit of the CRT, in a dot matrix type display handling fixed pixels such as a liquid crystal display, efficient information cannot be obtained and proper display is similarly not possible.
An object of the present invention is to provide a dot matrix type image display apparatus capable of properly displaying an image even if a non-registered image signal is input.
To solve the above disadvantages, an image display apparatus of the present invention comprises a characteristic detection means for detecting from an input image signal predetermined characteristics regarding the specification of the image signal including at least the number of vertical lines; a horizontal pixel number estimation means for multiplying said detected number of vertical lines with a predetermined constant to calculate an estimated value of the number of horizontal pixels; an A/D conversion means for successively sampling the signal of every horizontal period of said input image signal by a sampling cycle based on the above calculated estimated value of the number of the horizontal pixels and converting it into a digital image signal; a signal conversion means for converting said converted digital image signal to a display signal of a predetermined dot matrix type based on the configuration of a display means; and a display means of a dot matrix type for displaying the image based on the converted display signal.
In an image display apparatus having such a configuration, the characteristic detection means finds the number of vertical lines from the input image signal and the horizontal pixel number estimation means multiplies the found number of the vertical lines by a predetermined constant to estimate the number of horizontal pixels. Then, the A/D conversion means successively samples the signal at every horizontal period of the input image signal by a predetermined sampling cycle determined based on the estimated value of the number of horizontal pixels and converts it from an analog to digital format. The signal conversion means converts the thus generated digital image signal is converted to a display signal of a predetermined dot matrix type based on the configuration of the display means and displays it by the display means.
Preferably, the image display apparatus of the present invention further comprises a memory means in which information regarding specifications of said image signal including the number of horizontal pixels are stored for each of any plurality of types of image signals and an image signal identification means for comparing said detected predetermined characteristics with said information of image signals stored in advance to search for the same type of image signal as said input image signal from the plurality of types of image signals whose information is stored in advance; wherein said A/D conversion means performs said sampling by a sampling cycle based on said information regarding the number of horizontal pixels of the image signals stored in said memory means when an image signal of the same type as said input image signal is found and performs said sampling by a sampling cycle based on an estimated value of said calculated number of horizontal pixels when an image signal of the same type as said input image signal is not found.
Specifically, said horizontal pixel number estimation means multiplies said detected number of vertical lines with a predetermined constant between 1.6 to 1.85 when said input image signal is an image signal suitable to a display having an aspect ratio of 4:3; multiplies said detected number of vertical lines with a predetermined constant between 1.5 to 1.7 when said input image signal is an image signal suitable to a display having an aspect ratio of 5:4; and multiplies said detected number of vertical lines with a predetermined constant between 1.9 to 2.1 when said input image signal is an image signal suitable to a display having an aspect ratio of 16:9 so as to calculate the estimated value of the number of horizontal pixels.
More specifically, said display means is a liquid crystal display means.
Further, preferably, said signal conversion means performs conversion of said digital image signal based on said information regarding the specifications of the image signal stored in said memory means when an image signal of the same type as said input image signal is found and obtains information regarding the specifications of the image signal based on characteristics of said detected input image signal and performs conversion of said digital image signal based on the information when an image signal of the same type as the input image signal is not found.
Specifically, said signal conversion means obtains information regarding the specifications of the image signal in accordance with the GTF (generalized timing formula) established by the VESA (Video Electronics Standard Association) based on the characteristics of said detected input image signal when an image signal of the same type as the input image signal is not found.
More specifically, said characteristic detection means detects a vertical synchronization signal and a horizontal synchronization signal from said input image signal and counts the number of horizontal synchronization signals included in a vertical synchronization period to obtain said number of vertical lines.
Alternatively, specifically, said characteristic detection means detects a vertical synchronization signal and a horizontal synchronization signal from said input image signal, finds a horizontal frequency and vertical frequency, and divides the horizontal frequency by the vertical frequency to find the number of vertical lines.